FROMLIST: drm/bridge: analogix_dp: Don't read EDID if panel present

FROMLIST: drm/bridge: analogix_dp: Don't read EDID if panel present

If there's a panel connected to the analogix_dp bridge, rely on
the panel driver for modes, rather than reading EDID *and* calling
get_modes() on the panel.

This allows panels with a valid EDID to read it in the panel driver
(e.g. simple_panel), and panels with invalid EDID to homebrew modes
in their get_modes implementation.

BUG=chrome-os-partner:53565
TEST=Boot device and confirm the modes returned are from panel driver
     instead of EDID

[from https://patchwork.freedesktop.org/patch/107115/]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/374959
Commit-Ready: Chris Zhong <zyw@rock-chips.com>
Tested-by: Chris Zhong <zyw@rock-chips.com>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Change-Id: Ie07dd33e3c121215bf24394cfcb3fff8c7c746a5
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>